In a cardiac cycle, a pacemaker, an atrium, and a ventricle are excited one after another with changes of bioelectricity. Various forms of graphs indicative of electric potential changes can be derived from the body surface using an electrocardiograph (ECG) device, which are called electrocardiograms.
For ECG monitoring, lead wires and electrodes can be attached or adhered to the body surface of an individual to obtain ECG signals. When more leads are used, more lead wires and electrodes are also needed. For example, at least three lead wires and three electrodes may be needed for limb leads, and 10 lead wires and 10 electrodes may be needed for 12 leads.